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OCR for page 43
43 top mat steel depth was in excess of 2 pounds per cubic yard, Up until 1996, the systems were operated as a galvanic a cathodic protection system was reapplied after widening; cathodic protection system. At the start of the operations as otherwise, a dense concrete overlay was used. In two projects an impressed current system there were issues with the for bridge widening, a total of 27 bridge decks were evalu- remote monitoring and remote control of the system and ated. These bridge decks had been protected by cathodic many zones were not outputting sufficient current to meet the protection systems for a minimum of 10 years. A total of 10 100 mV shift criteria. The problems with the remote monitor- bridge decks did not require reapplication of the cathodic ing and control systems were worked out and the systems protection system; on 15 bridge decks the cathodic protection were outputting current density of 2.2 mA per square foot of was reapplied and 2 bridge decks were replaced. concrete surface area (54). The oldest operational system in Oregon is on the Cape Creek Bridge, which has been opera- The experiences of Missouri clearly indicate that the tional since 1989. application of cathodic protection not only extends the ser- vice life of the reinforced concrete structure but can revert it to a chloride contamination state, which does not require Conductive Paint cathodic protection. No other corrosion mitigation system, A conductive paint system had been operational on the with the exception of electrochemical chloride extraction, Yaquina Bay Bridge for 17 years when reported in 2004 (54). can do that. Two conductive paint systems were monitored by the FHWA-54 project and both of them were located in Virginia. Mixed Metal Oxide One was installed on the hammerheads of the bridge carrying I-95 over the James River in Richmond and the other was on Six mixed metal oxide systems were monitored under the the hammerheads of the bridge carrying I-81 over the Maury FHWA-54 project; the mesh form of the anode was used in River in Lexington. Both systems provided adequate protec- five and the ribbon was used in one. The mesh anodes were tion while they were operating. The conductive paint was installed on the decks of three bridge structures. The deck deteriorating owing to exposure to the elements and the sys- systems had been operational for 6 to 12 years by the end of tem on the I-95 bridges had reached the end of its service life the evaluation and were judged to be operating satisfactorily. after 9 years of operation, and the system in Lexington was The ribbon anode was installed on a bridge deck and was exhibiting signs of paint deterioration after 5 years of opera- documented to be performing well after 9 years of operation, tion. The systems on the bridges of I-95 were replaced and and in the survey it was reported to be operational at the age the Lexington Bridge was replaced. Although the conductive of 16. The mesh anode has been installed on marine substruc- paints may have a shorter service life, especially when exposed ture elements of several bridges in Florida and is either to the elements, it is fairly inexpensive to reapply the paint and encapsulated in gunite or installed in a jacket system. The extend the remaining service life. oldest of these is the gunite encapsulated system, which was in operation for 19 years at the time of reporting and had only minor repairs to correct failed gunite (53). The authors of the GALVANIC CATHODIC PROTECTION SYSTEM Florida report expect this type of system to provide a service life extension in the range of 50 years. The oldest operational There is a tendency for many agencies to use the galvanic system in Missouri was installed in 1989 and was operating sat- cathodic protection systems because they do not need the isfactorily after 19 years. Since 1990, Ontario has been using level of monitoring and maintenance that impressed current the mixed metal oxide mesh anodes on bridge decks with a cathodic protection systems require. These are finding appli- cementitious overlay and waterproofing and has had signifi- cation on marine substructure elements and superstructure cant success with this system. Service life is projected to be elements exposed to deicing salts. in the range of 25 to 30 years. Connecticut has 12 bridge deck systems that have been operational for 15 to 18 years. This Arc Sprayed Zinc anode material has proven to provide the longest extension in service life and has one of the highest current discharge Arc sprayed zinc is being used primarily on marine substruc- capacities among other available materials. ture and superstructure elements. Research has indicated that the resistance of the system can be maintained within accept- Arc Sprayed Zinc able limits if sufficient moisture is available. Direct wetting of the zinc system is most effective in maintaining the The second largest application of arc sprayed zinc in Oregon delivery of adequate current by the system (55). This anode is on the Yaquina Bay Bridge and protects 283,300 square is suitable for application above the tidal zone. On the drier feet of concrete surface area. This system was energized in superstructure elements where direct wetting of the system is 1996 and was monitored under the FHWA-54 effort until not possible, the zinc anodes suffice because corrosion rates 1998. The installation of the system on the arch spans was are generally lower in these locations and the galvanic sys- completed in 1991 and on the south approach spans in 1995. tems are able to provide adequate cathodic current. In Florida

OCR for page 43
44 alone, arc sprayed zinc has been applied in 36 projects and Zinc Mesh Anodes in a Jacket protects 677,053 square feet of concrete surface area. The old- est such system was installed in 1989 on the Niles Channel The zinc mesh anodes in a jacket have been used in Florida Bridge and was operational for 17 years. since 1994. To date, these types of galvanic cathodic protec- tion systems have been used on 51 projects and installed on Three systems were evaluated under the FHWA-54 pro- approximately 1,782 piles. At least 16 structures have these gram and all of them were installed on marine substructure systems, which have been in operation for more than 10 years. elements. The experimental system on the Queen Isabella FDOT has a program to monitor and maintain them and their Causeway in Texas was only 1 year old at the end of the proj- data to date indicate that, in general, these systems are pro- ect and was performing well. The Howard Frankland Bridge viding adequate protection. in Tampa and the Seven Mile Bridge in the Florida Keys had arc sprayed zinc systems that were 5 and 7 years old, respec- Overall Long-Term Performance tively, at the end of the evaluation. The Howard Frankland Bridge system was performing well; however, the Seven Cathodic protection systems that are properly designed, Mile Bridge was providing less than adequate protection. The installed in accordance with standard practice and good work- Seven Mile Bridge has epoxy-coated rebar and the cathodic manship, and adequately monitored and maintained have per- protection system was installed to provide protection to the formed well. The agencies that have committed to the use epoxy-coated rebar. of this technology and have made resources available have reaped the long-term benefits and have reduced their overall Over the last five years, Ontario has increasingly used arc maintenance costs. Several different types of cathodic protec- sprayed zinc and the aluminumzincindium alloy as cathodic tion systems have been demonstrated to provide service life protection anodes on piers, girders, and caps and their moni- extension of at least 20 years, and are expected to continue to toring data indicate good performance to date. provide protection.